Aluminum photographic surfaces

ABSTRACT

The impregnation of an anodized layer on aluminum with silver salts is greatly improved and facilitated by supplying the soluble silver salt (used as the means for eventual formation of silver halide in the pores of the anodized aluminum) as a solution in which the solvent is a combination of a minor amount of water and a major amount of highly polar organic liquids in which alkali chlorides show low or very limited solubility. By use of this improved technique, a shelf stable photosensitive article is obtained which is capable of yielding deep, lustrous blacks on exposure and development without the need for gold toning to obtain such a result.

United States Patent Horizons Research Incorporated ALUMINUM PHOTOGRAPHIC SURFACES 4 Claims, No Drawings [1.8. CI 96/86 R, 96/94 BF, 117/34 Int. Cl G03c 1/94 Field of Search 96/86 R, 94 BF; 117/34 References Cited UNITED STATES PATENTS 2,115,339 4/1938 Mason 96/86 2,766,119 10/1956 Freedmanetal...

2,126,017 8/1938 Jennyetal ABSTRACT: The impregnation of an anodized layer on aluminum with silver salts is greatly improved and facilitated by supplying the soluble silver salt (used as the means for eventual formation of silver halide in the pores of the anodized aluminum) as a solution in which the solvent is a combination of a minor amount of water and a major amount of highly polar organic liquids in which alkali chlorides show low or very limited solubility. By use of this improved technique, a shelf stable photosensitive article is obtained which is capable of yielding deep, lustrous blacks on exposure and development without the need for gold toning to obtain such a result.

ALUMINUM PHOTOGRAPHIC SURFACES THE PRIOR ART U.S. Pat. No. 2,766,] 19 defines the prior art and indicates the difficulties experienced by earlier workers in the field. These difficulties resided primarily in the inability to obtain a plate which exhibited any significant shelf life. As a consequence, it was required that the plate be sensitized immediately prior to the exposure. U.S. Pat. No. 2,766,! 19 describes a way to improve the shelf life by adding an organic hydrocolloid in one of the impregnating steps. As a consequence, the shelf life of the finished article was extended to several years. Recent experience has established that the shelf life of such a plate is at least years. However, through the fundamental problem of lack of storageability has been eliminated by the teachings of US. Pat. No. 2,766,119 the method described therein suffers from two serious defects. In order to carry out the procedure, an exceptionally high concentration of silver was required in the impregnating solutions to yield a meaningful amount of photosensitive silver salt in the pores of the anodized aluminum on completed processing. ln addition, the image obtained on development with a high contrast developer always exhibited brownish or sepia overtones. In order to obtain the jetblack rendition which is most desirable commercially, it is required that the silver image be toned with gold salts. Thus, the process is unduly expensive, not only because of the high concentration of silver in the solution which is required for impregnation, but also because of the use of the even more expensive gold solutions needed to produce the black rendition.

THE OBJECTS OF THE PRESENT INVENTION It is a primary object of this invention to yield a shelf-stable, silver-halide-type photosensitive anodized aluminum layer which on development and fixing yields a jetblack color without the need for gold toning.

it is a further object of this invention to diminish the amount of silver required to yield the desired jetblack color without the need for gold toning.

It is also an object of his invention to accelerate the technique of impregnation, thereby permitting operation with a lower silver content in the impregnation step while still 0btaining the jetblack color after development without the need for gold toning.

DESCRIPTION OF THE PROCESS in known processes of preparing an anodized layer on aluminum suitable as a base for impregnation with silver slats to render such a certain surface sensitive to light and capable of being developed and fixed after exposure so as to yield a permanent image, the aluminum metal is anodized, i.e. it is oxidized electrolytically under specific conditions. After anodizing the aluminum metal the surface exhibits a large number of pores. THe pores of the surface thus achieved are washed to remove the residues of the anodizing electrolyte, and then treated with a strong oxidizing agent to seal the bottom of the pores so that the bare aluminum'is not exposed. The pores are then impregnated with a water solution of a soluble silver salt which contains a minor amount of gelatin (in accordance with the teachings of U.S. Pat. No. 2,766,119) and after drying from the first impregnation solution, the silver salt is transformed to a halide, generally comprising a mixture of chloride-bromide-iodide or a mixture of bromide and iodide, through treatment of the previously silver salt impregnated base with an appropriate solution of an alkali halide. Normally, in order to ensure that no bare aluminum is exposed, the alkali halide solution also contains a small amount of oxidizing agent.

I have found that if the silver nitrate of the impregnating solution is dissolved in a solvent containing a minor amount of water and a major amount of a strongly polar organic solvent in which the alkali halide shows little or limited solubility, that not only are the desired objectives obtained, but also that the processing for yielding a finished plate is accelerated in view of the elimination of certain intermediate drying steps.

The organic portions of this solvent suitable for the purposes of the invention are listed in table 1. Each of these solvents is highly polar in character, completely miscible with water, and that most alkali halides exhibit limited solubility in such solvents. in the preferred practice of the invention, the solvent for the silver salt to be deposited in the pores of the anodized surface normally contains a minor amount of water, usually between 10 and 30 percent, in order to achieve the desired degree of solubility of the silver nitrate in such a solvent. The amount of water used is generally not sufiicient to have a major effect on the eventual solubility of the alkali halide. The balance of the solvent comprises one of the organic solvents listed'in table 1 or mixtures thereof. Silver nitrate concentrations useful for achieving the desired end results range between 6 grams by weight of silver nitrate to 20 grams by weight of silver nitrate per hundred cc. of solvent and the optimum range for the best results is between l2 grams of silver nitrate and 15 grams of silver nitrate per hundred cc. of solvent. The minimum time of immersion in this solution to achieve the desired results is approximately 30 seconds for plates anodized in the preferred manner and better results are obtained by extending the time of immersion from 1 minute up to a maximum of5 minutes.

TABLE 1 ORGANIC SOLVENTS FOR AgNO, Step SOLVENT Methyl Alcohol Ethyl Alcohol lsopropyl Alcohol Tert-butyl Alcohol Acetone Methyl Ethyl Ketone Glycol Monomethyl Ether Glycol Monoethyl Ether I :i mat-s For example, if a 20 percent solution of silver nitrate is utilized, an immersion time of 1 minute is ample, whereas'if a 6 percent solution of silver nitrate is utilized, an immersion time of 5 minutes is required to duplicate the results obtained with the shortened immersion in a 20 percent solution. in the preferred range of 12 to 15 percent silver nitrate, a second immersion is sufiicient for obtaining the desired results.

After removal of the anodized plate from the immersion in the silver nitrate solution, the excess liquid is removed from' the plate by squeegee and the treated plate immediately dipped without intervening drying into a solution containing alkali halide. No loss of silver salt develops as a consequence of this treatment and there appears to be no leaching or back solution. While I do not wish to be bound by any specific theory, it appears that in view of the retention in the pores of the anodized plate of a residual amount of the strongly polar organic solvent which carries the original silver nitrate and the limited solubility of the alkali halide in such a menstruumthe alkali halide precipitates almost immediately on contacting such retained liquid and effectively operates as a barrier towards the elution of silver nitrate out from the pores. Metathesis takes place almost immediately to deposit insoluble silver halide in the pores of he anodized surface. Thereafter,the plate may be washed with impunity and without fear of removal of such silver halide from these pores.

The preferred method of preparing the plate to make it act as a suitable receptor for the impregnation which has been described is electrolytic oxidation or, as it is generally designated commercially, anodizing. Thus, for example, aluminum may be anodized in an electrolyte make up of a mixture of oxalic acid and oxalates of alkali metals, at a pH of l to 5, a current density covering a range between 0.5 and amperes per square decimeter, and a temperature range between 40 and 75 C. Direct current anodizing is preferred. Anodized surfaces made in this way are hard, adherent and are highly absorbent for soaking up liquids and salts in solution. Anodizing under the conditions just described is generally continued for a time period sufficient to yield a thickness of the anodized layer of at least the order of 0.0002 inches and preferably up to a thickness of 0.005 inches. Under these conditions, the

time of anodizing is generally about 30 minutes. After the aluminum surface has been initiallyoxidized, it is then subjected to a chemical treatment involving powerful oxidation which makes certain that no metallic aluminum is exposed at the base of the pores. Useful energetic oxidizing agents for this purpose include chromic acid, solutions of alkali ferricyanides, dichromates, or chromates in concentration ranges of 0.01 to 10 percent. After washing and drying this double oxidized surface, the plate bearing the prepared oxidized aluminum surface is then dipped into the solutions which eventually produce the photosensitive salts of silver in the pores of the coating and not on the surface. Small amounts of oxidizing agents may be added during the photosensitive impregnation process to insure complete protection against undesired exposure of metallic aluminum, such exposure showing a spot defeet in finished plates which is not acceptable commercially.

In impregnating with the silver nitrate solutions and following such impregnation without drying, and then finishing the treatment with an alkali halide salt, both the silver nitrate solutions and the alkali halide solutions may contain small amounts of water-soluble oxidizing agents of the types just described for continued insurance against the presence of bare spots of aluminum.

A preferred slat of silver for achieving the desired result is silver nitrate and the preferred alkali halides are the sodium or potassium chlorides, bromides, or iodides. A preferred procedure is to apply the silver nitrate in solution, then a solution of an alkali chloride, and after the silver chloride has been formed in the oxide coating, the plate may be ripened in an alkali bromide or alkali iodide or combinations of the bromide and iodide. The amount of oxidizing agents used in combination with the soluble silver salt is very small, on the order of 0.01 to 0.03 percent of an alkali metal ferricyanide', dichromate, or chromate, as described in the above noted U.S. Pat. No. 2,766,119.

For the conversion of the soluble silver salt, e.g. nitrate, to silver halide, the potassium bromide or chloride are preferred, but other alkali halides can be used. For the silver halide forming impregnation, sodium chloride is preferred because of its highly limited solubility in the organic solvents listed in table 1. The alkali halide solutions utilized have concentrations in the range 'of to percent.

After formation of the silver halide salts in the pores, the plates are washed and dried and are then ready for use.

The photographic plate thus obtained is exposed to a pattern of light, developed and fixed in accordance with usual photographic practices, e.g. as described in the above noted U.S. Pat. The image may be toned with salts or the background dyed to achieve spacial effects in accordance with known practice and a final operation which is usually advisable is to seal the surface so that it is permanently resistant to abrasion and scratching. This consists of immersing the plate in boiling solutions 'of salts, such as sodium sulfate, sodium acetate, and the like for a period of about l0 minutes. The surface may also be sealed and waterproofed by the application of silicone polishes or various synthetic resins which may be cured on the surface.

Having described my invention, the following examples are indicative of my method of practice.

EXAMPLE 1 All anodized plates utilized in examples 2 and following were first given a preliminary oxidation treatment in a 5 percent solution of chromic acid in water at 60 C. for 5 seconds. The plates were washed in cold deionized water until all chromic acid was removed and then air dried.

All impregnation steps were carried out in the photographic darkroom using red safelight conditions.

EXAMPLE Z The dried preoxidized plate as prepared in example 1 was used as a base in the darkroom, 6 grams of silver nitrate were dissolved in a mixture of 80 cc. of isopropyl alcohol and 20 cc. of distilled water. In addition, 0.02 grams of potassium dichromate were also added to the solution and stirred until solution was complete. The dried anodized plate was soaked in this solution for 5 minutes, allowed to drain and the excess solution wiped from the surface with a rubber squeegee. Without intervening drying, the plate was then soaked for 1 minute in a solution containing 20 grams of sodium chloride and 3 grams of potassium dichromate in 100 cc. of distilled water. The surface was again squeegeed to remove any precipitate that might have developed on this surface and then the plate was washed in running water. The thoroughly washed plate was then oven dried at 50 and stored in the dark until used.

EXAMPLE 3 The same as example 2, except that 15 grams of silver nitrate were dissolved in 100 cc. of a mixture of 25 cc. of water and 75 cc. of isopropyl alcohol. In this case, the first impregnation was permitted to continue for 1 minute before squeegeeing and following with the treatment with the sodium chloride solution.

EXAMPLE 4 The same as example 2, except that after washing after the sodium chloride treatment step, the plate was placed in a bath containing 12 k grams of potassium ferricyanide, 10 grams of potassium bromide and 2 grams of sodium dichromate, all dissolved in a liter of water, and retained in this bath for l TABLE 2.SAl\lE AS, EXAMPLE 5, EXCEPT FOR CHANGES minute. After rinsing with running water, the wet plate was then immersed in a 1 percent solution of potassium bromide for 1 minute and was then washed thoroughly, dried at 50 C., and stored in the darkroom until used.

EXAMPLE 5 The same as example 4, except that in place of the 1 percent potassium bromide solution, the solution used consisted of a mixture of 1 percent potassium bromide and l percent potassium iodide dissolved in distilled water.

EXAMPLE 6 The same procedure'as described in example 3, except that the 1 percent potassium bromide bath used for ripening contained 0.01 percent of silver nitrate.

EXAMPLES 7- l4 BELOW NOTED Time of Example Watvr AgNO; immersion, N0. Organic solvent (00.) (grams) nnnutes 7 cc. methyl alcohol l5 8 4 85 cc. ethyl alcohol 15 8 4 80 cc. t-butyl alcohol 2O 8 4 80 cc.acctout- 20 8 4 80 ccimothyl ethyl ketonc. 20 8 4 cc. glycohnoiiomethyl- 10 8 I 4 ether. 13 90 cc. glycolmqpoethyl- 10 8 4 c ier. 30 cc. ethyl alcohol 30 cc. acetonc 30 cc. glycolmonoethyl- 10 8 4 ether.

EXAMPLES l5-23 TABLE 3.SAME AS EXAMPLE 5, EXCEl T FOR CHANGES BELOW NOTED Time of Example Water AgNOa immersion, No. Organic solvent (cc) (grams) seconds 15 80 cc. methyl alcohol 2O 14 90 16 80 cc. ethyl alcohol 20 14 90 17 75 cc. t-butyl alcol1ol 25 14 90 18 75 cc. acetone 25 14 90 19 .1 75 cc. niethylethyl 25 14 90 etone. 20 85 cc. glycolmonomethyl 15 14 90 ether. 21 85 cc. glycolmonoethyl- 15 14 90 cc. isopropy a co 0 22 "{45 cc. acetone 15 14 90 23 75 cc. isopropyl alcohol.... 15 15 90 All of the end products defined in examples 2 through 23 yield a shelf-stable-photosensitized plate which, after exposure to light, developing, fixing, washing ans sealing yields a jetblack image color Both aluminum or commercial aluminum base alloys are useful in the practice of this invention.

solution of at least one alkali metal halide. 2. The process of claim 1 in which the volume proportion of the polar organic liquid in the solvent is at least about twothirds of the solution and the volume proportion of water is not more than one-third of the solvent for the silver salt.

3. The process of claim 1 in which the silver salt is dissolved in a mixture of isopropanol and water in which the water does not exceed 15 percent by volume.

4. The process of claim 3 in which the silver salt is silver nitrate. 

2. The process of claim 1 in which the volume proportion of the polar organic liquid in the solvent is at least about two-thirds of the solution and the volume proportion of water is not more than one-third of the solvent for the silver salt.
 3. The process of claim 1 in which the silver salt is dissolved in a mixture of isopropanol and water in which the water does not exceed 15 percent by volume.
 4. The process of claim 3 in which the silver salt is silver nitrate. 